Date of Award

Summer 2019

Document Type

Open Access Dissertation

First Advisor

Roozbeh Behroozmand

Abstract

Existing evidence suggests that the brain facilitates motor responses to temporally predictable sensory inputs by generating more robust predictions about the timing of incoming stimuli to better estimate the next state of movement. In this context, previous studies have shown that motor responses are generated with faster reaction time in response to sensory stimuli with predictable compared to those with unpredictable temporal dynamics. However, our understanding of the underlying behavioral and neural mechanisms of temporal predictive mechanisms during movement production has remained limited by several factors. First, studies regarding temporal predictive mechanisms have mainly examined limb movement as a target modality and less is known about other motor modalities such as speech production. In addition, previous studies have primarily focused on investigating the temporal predictive mechanisms during movement initiation and our understanding of the nature of these mechanisms during movement inhibition has remained elusive. Moreover, most of the previous studies have examined young healthy adults to probe the underlying temporal processing mechanisms during movement and less is known about the effect of normal aging on the behavioral and neural correlates of these mechanisms in older adults.

This dissertation presents the results and discusses the findings of several studies that aimed to bridge these gaps by measuring the behavioral correlates of motor reaction time concurrent with recordings of neural activities using event-related potentials (ERPs) in two groups of younger and older adults while they performed speech and limb movement initiation and inhibition tasks in responses to temporally predictable and unpredictable sensory stimuli. Findings of these studies revealed that speech and limb motor reaction times are accelerated in response to incoming sensory stimuli with predictable temporal dynamics during both movement initiation and inhibition tasks. In addition, the results revealed that faster reaction times for initiating speech and limb movement were correlated with a significant attenuation of pre-motor ERP activities in response to temporally predictable vs. unpredictable stimuli, suggesting that these components may serve as a neural signature of temporal predictive mechanisms in the motor system. Moreover, the findings showed that ERP activities before limb movement inhibition were attenuated for predictable vs. unpredictable sensory stimuli whereas an opposite pattern of neural activities was observed for speech motor inhibition responses. Furthermore, behavioral findings revealed that older adults were slower than their younger counterparts only during speech motor initiation and inhibition tasks when the stimulus timing was unpredictable, but no such effect was observed during the limb motor reaction time task. Lastly, the results indicated that pre-motor ERP activity prior to the onset of speech, but not limb, movement initiation was significantly larger in older vs. younger adults when stimulus timing was unpredictable, but no difference was observed between the groups in response to temporally predictable sensory stimuli.

Overall, the findings of these studies suggest that common temporal predictive mechanisms may support speech and limb movement initiation in response to sensory stimuli and pre-movement ERPs may be a neural signature of these mechanisms. In contrast, for movement inhibition, findings revealed distinct patterns of premotor ERP activities for speech vs. limb movement, indicating the functional dissociations between these two modalities, particularly during movement inhibition. Finally, the findings of these studies suggest temporally and modality specific decline in the temporal predictive mechanisms of movement production in older adults and highlight the effect of normal aging on the behavioral and neural correlates of these mechanisms during speech and limb motor reaction time tasks.

Share

COinS